Angiotensin I-converting enzyme (ACE) converts the largely inactive decapeptide angiotensin I to the active octapeptide angiotensin II. ACE is a key component of the renin-angiotensin system that has long been suspected to play a role in the pathogenesis of hypertension and cardiovascular disease. The ACE gene spans 21 kilobases and consists of 26 exons, and two different mRNAs and endothelial and testicular ACE are transcribed from the ACE gene. Circulating ACE probably originates from proteolytic cleavage of the hydrophobic anchor and passive leakage of the membrane-bound enzyme. Normal serum ACE by spectrophotometric assay is very low (8.3-21.4 microliters/ml). The abnormally elevated ACE levels is indeed a diagnostic aid in sarcoidosis. The ACE gene has 287 base pair insertion/deletion polymorphism in intron 16. The ACE deletion polymorphism appears to be associated with increased risk for myocardial infarction in the Caucasian and Japanese population. Recently in multicenter clinical trials (SAVE), administration of inhibitors of ACE were shown to decrease cardiac events after myocardial infarction.